A2 exposure compensation chages flash exposure??

Coming form a Canon background, I've just bought a KM A2 and I am pleased with it. Much faster than my G3.
I noticed a strange behavior though that seems illogic to me:

let's say I want to take a picture in a dim light with flash. I also want to preserve the ambient light.

So, I set my A2 to aperture priority (as I was doing with my Canon). I pop up the flash. I see that slow sync is not an option in A2 menu, but I need to push the AE lock button (page 87 in manuial).

But since I don't want camera shake, I set an exposure compensation of -2 (dimmer background).

I would expect that exposure compensation DOES NOT change the flash exposure. but it seems in A2 this is not true (which is frustrating). A negative exposure compensation (ATTENTION: I'm not refferring to Flash exp comp!) will also make the flash weaker.